﻿using System;
using System.Security.Cryptography;

namespace CSharpExt.Util
{
    public class Crc64 : HashAlgorithm
    {
        public const UInt64 DefaultSeed = 0x0;

        private static readonly UInt64[] table = new UInt64[]
                                                     {
                                                         0x0000000000000000L, 0x01b0000000000000L, 0x0360000000000000L, 
                                                         0x02d0000000000000L, 0x06c0000000000000L, 0x0770000000000000L, 
                                                         0x05a0000000000000L, 0x0410000000000000L, 0x0d80000000000000L, 
                                                         0x0c30000000000000L, 0x0ee0000000000000L, 0x0f50000000000000L, 
                                                         0x0b40000000000000L, 0x0af0000000000000L, 0x0820000000000000L, 
                                                         0x0990000000000000L, 0x1b00000000000000L, 0x1ab0000000000000L, 
                                                         0x1860000000000000L, 0x19d0000000000000L, 0x1dc0000000000000L, 
                                                         0x1c70000000000000L, 0x1ea0000000000000L, 0x1f10000000000000L, 
                                                         0x1680000000000000L, 0x1730000000000000L, 0x15e0000000000000L, 
                                                         0x1450000000000000L, 0x1040000000000000L, 0x11f0000000000000L, 
                                                         0x1320000000000000L, 0x1290000000000000L, 0x3600000000000000L, 
                                                         0x37b0000000000000L, 0x3560000000000000L, 0x34d0000000000000L, 
                                                         0x30c0000000000000L, 0x3170000000000000L, 0x33a0000000000000L, 
                                                         0x3210000000000000L, 0x3b80000000000000L, 0x3a30000000000000L, 
                                                         0x38e0000000000000L, 0x3950000000000000L, 0x3d40000000000000L, 
                                                         0x3cf0000000000000L, 0x3e20000000000000L, 0x3f90000000000000L, 
                                                         0x2d00000000000000L, 0x2cb0000000000000L, 0x2e60000000000000L, 
                                                         0x2fd0000000000000L, 0x2bc0000000000000L, 0x2a70000000000000L, 
                                                         0x28a0000000000000L, 0x2910000000000000L, 0x2080000000000000L, 
                                                         0x2130000000000000L, 0x23e0000000000000L, 0x2250000000000000L, 
                                                         0x2640000000000000L, 0x27f0000000000000L, 0x2520000000000000L, 
                                                         0x2490000000000000L, 0x6c00000000000000L, 0x6db0000000000000L, 
                                                         0x6f60000000000000L, 0x6ed0000000000000L, 0x6ac0000000000000L, 
                                                         0x6b70000000000000L, 0x69a0000000000000L, 0x6810000000000000L, 
                                                         0x6180000000000000L, 0x6030000000000000L, 0x62e0000000000000L, 
                                                         0x6350000000000000L, 0x6740000000000000L, 0x66f0000000000000L, 
                                                         0x6420000000000000L, 0x6590000000000000L, 0x7700000000000000L, 
                                                         0x76b0000000000000L, 0x7460000000000000L, 0x75d0000000000000L, 
                                                         0x71c0000000000000L, 0x7070000000000000L, 0x72a0000000000000L, 
                                                         0x7310000000000000L, 0x7a80000000000000L, 0x7b30000000000000L, 
                                                         0x79e0000000000000L, 0x7850000000000000L, 0x7c40000000000000L, 
                                                         0x7df0000000000000L, 0x7f20000000000000L, 0x7e90000000000000L, 
                                                         0x5a00000000000000L, 0x5bb0000000000000L, 0x5960000000000000L, 
                                                         0x58d0000000000000L, 0x5cc0000000000000L, 0x5d70000000000000L, 
                                                         0x5fa0000000000000L, 0x5e10000000000000L, 0x5780000000000000L, 
                                                         0x5630000000000000L, 0x54e0000000000000L, 0x5550000000000000L, 
                                                         0x5140000000000000L, 0x50f0000000000000L, 0x5220000000000000L, 
                                                         0x5390000000000000L, 0x4100000000000000L, 0x40b0000000000000L, 
                                                         0x4260000000000000L, 0x43d0000000000000L, 0x47c0000000000000L, 
                                                         0x4670000000000000L, 0x44a0000000000000L, 0x4510000000000000L, 
                                                         0x4c80000000000000L, 0x4d30000000000000L, 0x4fe0000000000000L, 
                                                         0x4e50000000000000L, 0x4a40000000000000L, 0x4bf0000000000000L, 
                                                         0x4920000000000000L, 0x4890000000000000L, 0xd800000000000000L, 
                                                         0xd9b0000000000000L, 0xdb60000000000000L, 0xdad0000000000000L, 
                                                         0xdec0000000000000L, 0xdf70000000000000L, 0xdda0000000000000L, 
                                                         0xdc10000000000000L, 0xd580000000000000L, 0xd430000000000000L, 
                                                         0xd6e0000000000000L, 0xd750000000000000L, 0xd340000000000000L, 
                                                         0xd2f0000000000000L, 0xd020000000000000L, 0xd190000000000000L, 
                                                         0xc300000000000000L, 0xc2b0000000000000L, 0xc060000000000000L, 
                                                         0xc1d0000000000000L, 0xc5c0000000000000L, 0xc470000000000000L, 
                                                         0xc6a0000000000000L, 0xc710000000000000L, 0xce80000000000000L, 
                                                         0xcf30000000000000L, 0xcde0000000000000L, 0xcc50000000000000L, 
                                                         0xc840000000000000L, 0xc9f0000000000000L, 0xcb20000000000000L, 
                                                         0xca90000000000000L, 0xee00000000000000L, 0xefb0000000000000L, 
                                                         0xed60000000000000L, 0xecd0000000000000L, 0xe8c0000000000000L, 
                                                         0xe970000000000000L, 0xeba0000000000000L, 0xea10000000000000L, 
                                                         0xe380000000000000L, 0xe230000000000000L, 0xe0e0000000000000L, 
                                                         0xe150000000000000L, 0xe540000000000000L, 0xe4f0000000000000L, 
                                                         0xe620000000000000L, 0xe790000000000000L, 0xf500000000000000L, 
                                                         0xf4b0000000000000L, 0xf660000000000000L, 0xf7d0000000000000L, 
                                                         0xf3c0000000000000L, 0xf270000000000000L, 0xf0a0000000000000L, 
                                                         0xf110000000000000L, 0xf880000000000000L, 0xf930000000000000L, 
                                                         0xfbe0000000000000L, 0xfa50000000000000L, 0xfe40000000000000L, 
                                                         0xfff0000000000000L, 0xfd20000000000000L, 0xfc90000000000000L, 
                                                         0xb400000000000000L, 0xb5b0000000000000L, 0xb760000000000000L, 
                                                         0xb6d0000000000000L, 0xb2c0000000000000L, 0xb370000000000000L, 
                                                         0xb1a0000000000000L, 0xb010000000000000L, 0xb980000000000000L, 
                                                         0xb830000000000000L, 0xbae0000000000000L, 0xbb50000000000000L, 
                                                         0xbf40000000000000L, 0xbef0000000000000L, 0xbc20000000000000L, 
                                                         0xbd90000000000000L, 0xaf00000000000000L, 0xaeb0000000000000L, 
                                                         0xac60000000000000L, 0xadd0000000000000L, 0xa9c0000000000000L, 
                                                         0xa870000000000000L, 0xaaa0000000000000L, 0xab10000000000000L, 
                                                         0xa280000000000000L, 0xa330000000000000L, 0xa1e0000000000000L, 
                                                         0xa050000000000000L, 0xa440000000000000L, 0xa5f0000000000000L, 
                                                         0xa720000000000000L, 0xa690000000000000L, 0x8200000000000000L, 
                                                         0x83b0000000000000L, 0x8160000000000000L, 0x80d0000000000000L, 
                                                         0x84c0000000000000L, 0x8570000000000000L, 0x87a0000000000000L, 
                                                         0x8610000000000000L, 0x8f80000000000000L, 0x8e30000000000000L, 
                                                         0x8ce0000000000000L, 0x8d50000000000000L, 0x8940000000000000L, 
                                                         0x88f0000000000000L, 0x8a20000000000000L, 0x8b90000000000000L, 
                                                         0x9900000000000000L, 0x98b0000000000000L, 0x9a60000000000000L, 
                                                         0x9bd0000000000000L, 0x9fc0000000000000L, 0x9e70000000000000L, 
                                                         0x9ca0000000000000L, 0x9d10000000000000L, 0x9480000000000000L, 
                                                         0x9530000000000000L, 0x97e0000000000000L, 0x9650000000000000L, 
                                                         0x9240000000000000L, 0x93f0000000000000L, 0x9120000000000000L, 
                                                         0x9090000000000000L
                                                     };

        private readonly UInt64 seed;
        private UInt64 hash;

        public Crc64()
        {
            seed = DefaultSeed;
            Initialize();
        }

        public Crc64(UInt64 seed)
        {
            this.seed = seed;
            Initialize();
        }

        public override int HashSize
        {
            get { return 64; }
        }

        public override void Initialize()
        {
            hash = seed;
        }

        protected override void HashCore(byte[] buffer, int start, int length)
        {
            hash = CalculateHash(hash, buffer, start, length);
        }

        protected override byte[] HashFinal()
        {
            byte[] hashBuffer = UInt64ToBigEndianBytes(hash);
            HashValue = hashBuffer;
            return hashBuffer;
        }

        public static UInt64 Compute(UInt64 seed, byte[] buffer)
        {
            return CalculateHash(seed, buffer, 0, buffer.Length);
        }

        private static UInt64 CalculateHash(UInt64 seed, byte[] buffer, int start, int size)
        {
            UInt64 crc = seed;

            for (int i = start; i < size; i++)
                unchecked
                {
                    crc = (crc >> 8) ^ table[(buffer[i] ^ crc) & 0xff];
                }

            return crc;
        }

        private byte[] UInt64ToBigEndianBytes(UInt64 x)
        {
            return new byte[]
                       {
                           (byte) ((x >> 56) & 0xff), 
                           (byte) ((x >> 48) & 0xff), 
                           (byte) ((x >> 40) & 0xff), 
                           (byte) ((x >> 32) & 0xff), 
                           (byte) ((x >> 24) & 0xff), 
                           (byte) ((x >> 16) & 0xff), 
                           (byte) ((x >> 8) & 0xff), 
                           (byte) (x & 0xff)
                       };
        }
    }
}